As an image forming apparatus such as a copier and a printer, there is an apparatus such that the image forming rate is comparatively slow such as ten and several sheets/min. to twenty and several sheets/min. and sheets of paper after image forming are ejected into an intra-body paper ejection unit of the apparatus. In some image forming apparatus having such an image forming rate, to retain the paper ejection property into the paper ejection unit satisfactorily, the paper ejection rollers are provided with a corrugation function, and sheets of paper are stiffened, thus regular paper ejection is realized.
On the other hand, in some image forming apparatus, an optional device such as a finisher having a function for sorting and grouping sheets of paper after image forming or stapling and bundling them or a job separator, in a multiple functional peripheral (hereinafter abbreviated to MFP), for separating and ejecting sheets of paper after image forming by a copier and sheets of paper after image forming by a printer is mounted. In an image forming apparatus, for example, having a finisher as an optional device, if the paper ejection rollers are provided with a corrugation function and sheets of paper Pare stiffened, the sheets of paper are apt to be jammed in the relay conveying path from the paper ejection rollers to the finisher. Therefore the paper ejection rollers are generally set not to provide the corrugation function, when using an optional device.
However, even in an image forming apparatus optionally having the finisher like this, without using the optional device, sheets of paper may be ejected using the paper ejection unit on the apparatus body side. However, in the image forming apparatus having the optional device, if it is intended to eject sheets of paper into the paper ejection unit on the apparatus body side, since the paper ejection rollers have no corrugation function, the sheets of paper cannot be stiffened and there is a fear that at the time of paper ejection, the rear end of some sheet of paper may be left at the position of the paper ejection rollers. Particularly, if the height of the paper ejection area is restricted like the intra-body paper ejection unit, sheets of paper may be ejected upward above the horizontal line, and at this time, the rear end of each sheet of paper P is apt to be left at the position of the paper ejection rollers. If the rear end of a preceding sheet of paper is left at the position of the paper ejection rollers like this, the succeeding sheet of paper is caught by the rear end of the preceding sheet of paper at the position of the paper ejection rollers, thus jamming of sheets of paper may be caused.
Therefore, in Japanese Patent Application 8-241010, an apparatus is disclosed that regardless of the image forming rate, after ending of image forming, sheets of paper are ejected at a faster rate than the image forming rate.
However, since the conventional apparatus has a torque limiter on the paper ejection roller pair, before the rear end of a transfer member passes the fixing roller pair, the conveying rate by the fixing roller pair can be controlled, though the conveying rate is always increased when the transfer member passes the fixing roller pair and the load on the sheets of paper by the fixing roller pair is removed. Namely, the conventional apparatus does not speed up and drive the paper ejection roller pair whenever necessary. Therefore, for example, the paper ejection rate must be increased, when ejecting sheets of paper toward the intra-body paper ejection unit, though a problem arises that it cannot be applied to a paper ejection unit of an apparatus required to keep the paper ejection rate almost equal to the image forming rate, when ejecting sheets of paper toward the finisher which is an optional device.
Therefore, in an image forming apparatus having an optional device, an image forming apparatus and a paper ejection method thereof for smoothly ejecting sheets of paper after fixing to either of the optional device side and intra-body paper ejection unit side free of paper jamming are desired.